Streaky artefacts, subsurf, how to avoid?
Avoid using n-gons (polygons with more than 4 vertices) those will not subdivide nicely..



Get rid of it (and the one on the other side of the object)

Add one more loop cut (so that you have an even number of vertices in the edge loop)

Select the edge ring, use Grid fill and set the span to something that makes sense.

Grid fill will create proper topology based on quads.

Repeat grid fill on the other side of the object.